Congestion control in a wireless communication system using the battery level

ABSTRACT

A method for congestion control in the uplink of a wireless communication system having a wireless transmit/receive unit (WTRU) and a radio network controller (RNC) begins by receiving an interference report for each user. The average noise rise for each user calculated and congestion relieving measures are implemented based upon the average noise rise and the WTRU battery level. A method for congestion control in the downlink of a wireless communication system having a WTRU and a RNC begins by receiving a transmission power report for each user. The transmission power for each user is calculated, and congestion relieving measures are implemented based upon the average transmission power and the WTRU battery level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. patent application Ser. No.10/726,426 filed Dec. 3, 2003 which in turn claims benefit of U.S.Provisional Application No. 60/454,081, filed Mar. 11, 2003, which areincorporated by reference as if fully set forth herein.

FIELD OF INVENTION

The present invention relates generally to wireless transmit/receiveunit (WTRU) battery conservation in wireless communications systems, andmore particularly, to a method of achieving WTRU battery conservationwith assistance from the network and from radio resource management(RRM).

BACKGROUND

It is known that battery life for a WTRU is an important aspect of thequality of service that an end user perceives, and any measure thatcould achieve battery savings is a desirable accomplishment in wirelesscommunication system design. Some of the existing systems and methodsfor conserving battery power relate to reducing the power of at leastpart of the WTRU to conserve battery life. For example, in U.S. Pat. No.5,539,925, a base station sends a signal to a mobile station to turn offthe mobile station for a length of time communicated in the message. Atthe end of the “off” period, the mobile station will automaticallyrestart itself to determine whether it needs to remain active or whetherit can be turned off for an additional period.

U.S. Pat. No. 6,463,042 relates to a method in which a wireless terminalreceives a header packet and estimates the power level of the headerpacket. The wireless terminal then receives a portion of a followingdata packet, and estimates the power level of the data packet. Acomparison is made between the power level of the header packet and thepower level of the data packet. If the power levels are approximatelyequal, then the wireless terminal will receive and process the remainderof the data packet. If the power level of the header packet is greaterthan the power level of the data packet, then this is an indication thatthe base station is operating in quasi-discontinuous transmission(Q-DTX) mode and that the wireless terminal can ignore the remainder ofthe data packet and put some of the components into a low power mode.

In U.S. Pat. No. 6,463,307, a hibernation request is made by either thebase station or the mobile terminal. Parameters relating to thehibernation period, including when to wake the mobile terminal to checkfor paging messages or whether the mobile terminal has a data packet tosend, are then set by the base station and transmitted to the mobileterminal. Once the hibernating period has ended, if there are anywaiting paging messages, the mobile terminal is awakened and the pagingmessages are checked. If there are no paging messages, then adetermination is made whether the mobile terminal has any pending datapackets to send. If there are pending data packets, then the mobileterminal is awakened and the packets are sent. If there are no pendingpackets, then the mobile terminal returns to the hibernation mode.

The systems and methods described above relate only to the powering-downof components to conserve battery power, and not to methods forconserving battery power while the WTRU is actively transmitting. Itwould, therefore, be desirable to achieve battery savings when the WTRUis active.

SUMMARY

The present invention enables the radio resource management (RRM) in theradio network side to reduce wireless transmit/receive unit (WTRU)battery consumption. The WTRU reports its battery level information tothe network. The RRM in the network can then make informed decisions tomaximize the battery life of the WTRU while still maintaining therequired quality of service (QoS) and system capacity. Based on reportedbattery levels, different RRM actions can be taken relating to calladmission control, congestion control, user link maintenance, handover,power control, block error rate (BLER) target, and applicationconfiguration. The invention is described making reference to auniversal mobile telecommunication system (UMTS) frequency-divisionduplex (FDD)/time-division duplex (TDD) system, but is applicable to anywireless system, including IEEE 802.11 and global system for mobilecommunications (GSM).

A method for congestion control in the uplink of a wirelesscommunication system having a WTRU and a RNC begins by receiving aninterference report for each user. The average noise rise for each usercalculated and congestion relieving measures are implemented based uponthe average noise rise and the WTRU battery level.

A method for congestion control in the uplink of a wirelesscommunication system having a WTRU and a RNC begins by receiving aninterference report for each user. The average noise rise for each useris calculated, and the average noise rise is compared to a ratereduction threshold. If the average noise rise is greater than the ratereduction threshold, then rate reduction is performed for the userhaving the highest interference level, and the method terminates. If theaverage noise rise is less than the rate reduction threshold, then theaverage noise rise is compared to a rate recovery threshold. If theaverage noise rise is less than the rate recovery threshold, then theusers are ranked based on interference level from lowest to highest intoa candidate list. The user with the lowest interference level isselected from the candidate list and the selected user's WTRU batterylevel is checked. If the battery level is below the low level, then raterecovery is performed for the selected user and the method terminates.If the battery level is above the low level, then selecting the nextuser from the candidate list is selected and that user's battery levelis checked.

A method for congestion control in the downlink of a wirelesscommunication system having a WTRU and a RNC begins by receiving atransmission power report for each user. The transmission power for eachuser is calculated, and congestion relieving measures are implementedbased upon the average transmission power and the WTRU battery level.

A method for congestion control in the downlink of a wirelesscommunication system having a WTRU and a RNC begins by receiving atransmission power report for each user. The transmission power for eachuser is calculated and the average transmission power is compared to arate reduction threshold. If the average transmission power is greaterthan the rate reduction threshold, then the average transmission poweris compared to a rate recovery threshold. If the average transmissionpower is greater than the rate recovery threshold, then rate recovery isperformed for the user with the lowest transmission power and the methodterminates. If the average transmission power is less than the ratereduction threshold, then the users are ranked based on transmissionpower from highest to lowest into a candidate list. The user with thehighest transmission power is selected from the candidate list and theselected user's WTRU battery level is checked. If the battery level isbelow the low level, then rate reduction is performed and the methodterminates. If the battery level is above the low level, then the nextuser is selected from the candidate list and that user's battery levelis checked.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way of exampleand to be understood in conjunction with the accompanying drawingswherein:

FIG. 1 illustrates radio network controller (RNC) RRM actions accordingto WTRU battery level;

FIG. 2 is a flow chart of the RNC RRM behavior upon receiving the WTRUbattery level;

FIG. 3 is a flowchart of a call admission control procedureincorporating checking the WTRU battery level;

FIG. 4 is a flowchart of a congestion control procedure incorporatingchecking the WTRU battery level;

FIGS. 5 a-5 c are flowcharts of user link maintenance proceduresincorporating checking the WTRU battery level; and

FIG. 6 is a flowchart of a handover procedure incorporating checking theWTRU battery level.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

An implementation of the invention is described in the followingpreferred embodiment, which is applicable to a UMTS (FDD/TDD) system.The invention is, however, applicable to any wireless system including,e.g., IEEE 802.11 and GSM. Hereafter a WTRU includes, but is not limitedto, a user equipment, a mobile station, a fixed or mobile subscriberunit, a pager, or any other type of device capable of operating in awireless environment. When referred to hereafter, a base stationincludes, but is not limited to, a base station, a Node-B, a sitecontroller, an access point, or other interfacing device in a wirelessenvironment.

FIG. 1 shows the exchange of information in a UMTS system 100, includinga WTRU 102 and an RNC 104. The WTRU 102 reports its battery level to thenetwork as follows. The RNC 104 requests the WTRU 102 to report thebattery level measurement by sending a Measurement Control Message 110in the downlink. In the message 110, the RNC 104 configures the WTRU 102with the measurement reporting criteria, such as the frequency ofreporting for periodic-based reporting or the threshold forthreshold-based reporting. The WTRU 102 reports its battery level bysending a Measurement Report Message 112 according to the reportingcriteria dictated by the RNC 104. In order to conserve battery power,the report message 112 can be transmitted along with other measurements.For example, in UMTS networks, the battery level can be reported in amanner similar to any other measurement (i.e., via radio resourcecontrol (RRC) signaling).

The information contained in the report message 112 can include thenumber of remaining minutes of talk time and the number of remainingminutes of idle time. This number can be either an instantaneous valuebased on the current transmission environment and current type ofservice (e.g., voice or data), or an average value based on theconditions for the last X minutes. Alternatively, the reported batterylevel can be the percentage of available battery power remaining. TheWTRU 102 can be set to send the report message 112 periodically, or tosend the report message 112 when a threshold is reached. The periodicreporting can range from one second to ten minutes, with a preferreddefault value of one minute. For the threshold based reporting, the WTRUmay take frequent measurements, but will only send a measurement reportto the RNC when a certain threshold is crossed. The types of evaluatedthresholds include low, medium, and high thresholds, and will beexplained in detail below.

The RRM in the RNC 104 makes informed decisions based on the reportedbattery level of the WTRU 102. In general, the measurements used by theRRM to make a decision are those typically used in the art in connectionwith each type of decision, with the battery level of the WTRU 102 beingused as an additional criterion. Some of the other measurements used bythe RRM include downlink interference signal code power (ISCP), receivedsignal code power (RSCP), and pathloss.

The procedures affected by the battery level measurement will bediscussed in greater detail below. Viewed as a signal exchange betweenthe WTRU 102 and the RNC 104, the admission control procedure 120 istriggered by an admission request 122 sent by the WTRU 102. Theadmission control 120 indicates whether a call has been admitted bysending an admission response 124. A congestion control procedure 130will configure the WTRU 102 for a new transmission rate by sending asignal 132. A link maintenance procedure 140 will configure the WTRU 102for a new transmission rate by sending a signal 142. A handoverprocedure 150 will configure the WTRU 102 for handover by sending asignal 152. A power control procedure 160 will change the BLER target ofthe WTRU 102 by sending a signal 162.

FIG. 2 describes the RRM behavior 200 in the RNC 104 upon receiving thebattery level report message 112 from the WTRU 102. The RRM in the RNC104 first receives the WTRU battery measurement report message 112 (step202). The RNC RRM then updates the WTRU battery level parameter andstores it in a database (step 204). All other procedures have access tothis parameter, since the procedure behavior changes according to theWTRU battery level as explained in connection with each procedure below.Three battery level thresholds are used as triggers: low, medium, andhigh. These thresholds are the same as those mentioned above inconnection with the threshold-based battery level reporting. It shouldbe understood by those of skill in the art that the specific batterylevels and thresholds are design parameters that will vary with eachimplementation. Accordingly, these specific levels and thresholds willnot be described hereinafter.

The WTRU battery level is checked to determine if it is below the lowthreshold (step 206). If the battery level above the low threshold, thenthe WTRU battery level is checked (step 210) to determine if it is abovethe medium threshold. The higher the BLER target is, the higher thetransmission power that is needed and the battery will be drainedfaster. Therefore, it is desirable to adjust the BLER target based onthe current battery level. If the battery level is below the mediumthreshold, the current BLER target is maintained (step 212), and theprocedure is terminated (step 214).

If the battery level is above the medium threshold (step 210), the BLERtarget is set to the “high quality BLER” target (step 220). Next, thecurrent level of compression is evaluated (step 222). If the currentlevel of compression is the highest level of compression, then switch tothe lower level of compression (step 224) and terminate the procedure(step 214). Otherwise, maintain the current compression level andterminate the procedure (step 214).

If the WTRU battery level is below the low threshold (step 206), thenthe BLER target is set to the “low quality BLER” target (step 230) toextend the battery life. Next, link maintenance is triggered (step 232)to reduce the battery consumption rate, as explained below. Theapplication configuration and the compression level are adjusted (step234) to conserve battery power, as explained below. The procedure thenterminates (step 214).

Call Admission Control

Referring now to FIG. 3, the Call Admission Control (CAC) procedure 300begins by triggering CAC (step 302), which is done when the WTRU 102requests call admission from the RNC 104 (signal 122 in FIG. 1). Thenthe WTRU's battery level is checked (step 304). The next step taken bythe CAC procedure 300 depends directly upon the battery level andwhether the current call is real time (shown as “RT” in FIG. 3) ornon-real time (shown as “NRT” in FIG. 3).

If the battery level is low, CAC will only allow handover into a cell atthe guaranteed bit rate for real time calls, and will only allowhandover into the cell at the lowest bit rate (TFC1) for non-real timecalls (step 306). If the battery level is medium, CAC will only admitcalls at the guaranteed bit rate for real time calls, and will admit atTFC2 (the second lowest bit rate) or a lower bit rate for non-real timecalls(step 308). If the battery level is high, for both real time andnon-real time calls, CAC will admit the call at the maximum bit rate orlower (step 310). The CAC behavior according to the battery level issummarized in the following table. TABLE 1 CAC behavior according tobattery level. Battery CAC behavior CAC behavior level (real timeservices) (non-real time services) 1. Low Only allow handover into Onlyallow handover into the cell and consider the the cell and consider TFC1guaranteed bit rate for (lowest rate) for admission the admissiondecision decision for handover. and physical resource Assign physicalresources assignment. No other types based on the accepted bit ofaccesses are admitted. rate. No other types of accesses are admitted. 2.Medium Consider the guaranteed Consider TFC2 (second bit rate only forthe lowest rate) or lower for admission decision and admissiondecisions. Assign assign physical physical resources based on resourcesbased on the the accepted bit rate. guaranteed bit rate. (Where TFC4 bitrate > TFC3 bit rate > TFC2 bit rate > TFC1 bit rate > 0.) 3. HighConsider the maximum Consider the maximum bit bit rate and below forrate and below for the the admission decision admission decision and andassign physical assign physical resources resources based on the basedon the accepted bit accepted bit rate. rate.

After the bit rate determination has been made according to the currentWTRU battery level (steps 306, 308, or 310), the CAC procedure 300proceeds to step 312, where the cell load is checked to determine theallowable call admission bit rate. The accepted bit rate for the call ischosen by selecting the lower admission rate as determined by thebattery level and the cell load (step 314). Lastly, the physicalresources required for the call are allocated (step 316) and theprocedure terminates (step 318).

Besides the traditional criteria used to decide whether or not to admitthe user and the bit rate for admission (e.g., interference, carrierpower, cell load), the RNC 104 also adjusts the assigned bit ratedepending on the WTRU battery level. The criteria that are evaluated forCAC depend on the procedure design and can vary, per known CACprocedures.

Also, code fragmentation in TDD is minimized for WTRUs with a lowbattery level. There are usually multiple solutions to assign theOrthogonal Variable Spreading Factor (OVSF) codes required by a call, interms of the number of timeslots used and which codes to use in thetree. The fewer timeslots that are used, the lower the codefragmentation is. To minimize code fragmentation, the RNC RRM shouldallocate the codes in as few timeslots as possible. This reduces thepossibility that the WTRU 102 raises its power level when it is far fromthe base station. Once the call has been admitted, the RNC 104 sends aresponse message to the WTRU (signal 124 in FIG. 1).

Congestion Control

Congestion control performs rate reduction and rate recovery in both theuplink and the downlink. For the present invention, the WTRU's batterylevel is considered when performing rate recovery in the uplink and ratereduction in the downlink. FIG. 4 shows a flow chart of a congestioncontrol procedure 400 in accordance with the present invention. It isnoted that the criteria used in the congestion control procedure 400depend upon the design of the procedure. FIG. 4 shows a slow congestioncontrol procedure, which uses the average noise rise in the uplink andthe average transmit power in the downlink as criteria to decide whetheror not to trigger rate control. It is to be understood that the slowcongestion control procedure is only an example, and that the presentinvention is equally applicable to any congestion control procedure.

Referring now to FIG. 4, the congestion control procedure 400 begins byreceiving measurement reports for interference and transmission powerfor each user (step 402). Next, the average noise rise in the uplink andthe transmit power in the downlink are calculated for all users (step404). These measurements are stored at the RNC, and are used severaltimes during this procedure. When evaluating the uplink, a determinationis made whether the average noise rise exceeds the threshold for ratereduction (step 406). If the average noise rise is above the ratereduction threshold, then rate reduction is performed for the user withthe highest interference level (step 408) and the procedure terminates(step 409).

If the average noise rise is below the rate reduction threshold (step406), a separate determination is made comparing the average noise riseto the threshold for rate recovery (step 410). If the average noise riseis above the rate recovery threshold, then there is no need to invokerate recovery (step 412) and the procedure terminates (step 409). If theaverage noise rise is below the rate recovery threshold, then the userwith the lowest measured interference is selected (step 414). As notedabove, the interference is measured for all users in step 402, and canbe sorted either in step 402 or step 414. Next, the selected user's WTRUbattery level is checked to determine whether it is below the lowbattery level (step 416). If the battery level is above the low level,then rate recovery is performed for the selected user (step 418) and theprocedure terminates (step 409). If the battery level is below the lowlevel, then the next user in the candidate list for rate recovery isselected (step 420) and step 416 is repeated.

On the downlink, the average transmit power is compared to the thresholdfor rate reduction (step 430). If the average transmit power is belowthe rate reduction threshold, a separate determination is made comparingthe average transmit power to the threshold for rate recovery (step432). If the average transmit power is above the rate recoverythreshold, then there is no need to invoke rate control (step 434) andthe procedure terminates (step 409). If the average transmit power isbelow the rate recovery threshold, then rate recovery is performed forthe user with the lowest transmit power (step 436) and the procedureterminates (step 409). As noted above, the transmission power for eachuser is stored in step 402, and can be sorted either in step 402 or step436.

If the average transmit power is above the rate reduction threshold(step 430), then the user with the highest transmit power is selected(step 438). Next, the selected user's WTRU battery level is checked todetermine whether it is below the low battery level (step 440). If thebattery level is above the low level, then rate reduction is performedfor the selected user (step 442) and the procedure terminates (step409). If the battery level is below the low level, then the next user inthe candidate list for rate reduction is selected (step 444) and step440 is repeated.

In the procedure 400 on the uplink, if the RNC 104 has detected that thecongestion situation has been relieved (the average noise rise is lowerthan the threshold for rate recovery), the RNC 104 uses the batterylevel of the WTRU 102 as an additional criterion. Increasing the uplinktransmission rate drains the battery faster, because a highertransmission rate uses more power than a lower transmission rate. Thecongestion control ranks the WTRUs 102 according to their interferencelevel from low interference to high interference. The congestion controlthen selects the WTRU 102 with the lowest interference level. If theselected WTRU's battery level is below the low threshold, the congestioncontrol should pick the next WTRU 102 in the candidate list. If thebattery level of the WTRU 102 is greater than the low level, then raterecovery can be performed.

In the procedure 400 on the downlink, the RNC 104 detects congestionbased on the average value of recently received measurements. Oncecongestion is detected (the average transmit power is greater than thethreshold for rate reduction), the RNC 104 chooses the user with highesttransmit power for rate reduction. Decreasing the downlink receiving bitrate drains the battery faster because the WTRU 102 requires additionaltime to receive the same amount of data. Therefore, the RNC 104 uses thebattery level of the WTRU 102 as an additional criterion for decidingwhether to implement rate reduction. If the selected WTRU's batterylevel is below the low threshold, the congestion control should pick thenext WTRU 102 in the candidate list. Otherwise, rate reduction can beperformed for the selected WTRU. If the average transmit power is lowerthan the threshold for rate recovery, rate recovery should be conducted.Increasing the downlink receiving bit rate reduces the time for WTRU 102to receive the same amount of data, thus extending battery life.Therefore, WTRU 102 battery level is not a criterion for rate recoveryin the downlink.

Once the rate reduction or rate recovery is performed at the RNC 104,the RNC 104 reconfigures the WTRU 102 for the new rate (signal 132 inFIG. 1).

User Link Maintenance

Referring now to FIGS. 5 a-5 c, the user link maintenance procedure canbe triggered by three different events: (1) upon receipt of a batterylevel measurement report at the RNC, (2) upon receipt of the VVTRUtransmit power measurement on the uplink, and (3) upon receipt of thecode transmit power measurement on the downlink.

FIG. 5 a shows a user link maintenance procedure 500 that is performedupon receipt of a battery level measurement report (step 502). Adetermination is made whether the WTRU battery level is below the lowlevel (step 504). If the battery level is below the low level, then theuser's bit rate is decreased if operating in the uplink and the bit rateis increased if operating in the downlink (step 506) and the procedureterminates (step 507).

If the battery level is above the low level (step 504), then a separatedetermination is made whether the battery level is above the high level(step 508). If the battery level is below the high level, then there isno need to invoke link rate control (step 510) and the procedureterminates (step 507). If the battery level is above the high level,then a separate determination is made whether the user link rate wasreduced by another rate reduction procedure due to the triggering of abattery level measurement report (step 512). If the link rate was notpreviously reduced, then there is no need to invoke link rate control(step 510) and the procedure terminates (step 507). If the link rate waspreviously reduced, then a determination is made whether thetransmission power and the measured interference are low (step 514). Ifboth the transmission power and the measured interference are not low,then there is no need to invoke link rate control (step 510) and theprocedure terminates (step 507). If both the transmission power and themeasured interference are low, then rate recovery is performed, in whichthe uplink and downlink rates for the user are restored to the lastrates used before the rate reduction (step 516) and the procedureterminates (step 507).

FIG. 5 b shows a user link maintenance procedure 520 that is performedupon receipt of the WTRU transmit power in the uplink (step 522). TheWTRU transmit power is checked to determine if it is above the thresholdfor rate reduction (step 524). If the transmit power is above the ratereduction threshold, then rate reduction is performed (step 526) and theprocedure terminates (step 527). If the transmit power is below the ratereduction threshold (step 524), then a separate determination is madewhether the WTRU transmit power is below the threshold for rate recovery(step 528). If the transmit power is below the rate recovery threshold,then another determination is made whether the WTRU battery level isbelow the low level (step 530). If the battery level is above the lowlevel, then rate recovery is performed (step 532) and the procedureterminates (step 527). If the battery level is below the low level, thenrate recovery is not performed (step 534) and the procedure terminates(step 527). If the transmission power is above the threshold for raterecovery (step 528), then rate recovery is not performed (step 534) andthe procedure terminates (step 527).

FIG. 5 c shows a user link maintenance procedure 540 that is performedupon receipt of the code transmit power measurement in the downlink(step 542). The code transmit power is checked to determine if it isabove the threshold for rate reduction (step 544). If the code transmitpower is below the rate reduction threshold, a determination is madewhether the code transmit power is below the threshold for rate recovery(step 546). If the code transmit power is above the rate recoverythreshold, then there is no need to invoke link rate control (step 548)and the procedure terminates (step 549). If the code transmit power isabove the rate recovery threshold, then rate recovery is performed (step550) and the procedure terminates (step 549).

If the code transmit power is above the rate reduction threshold (step544), then the WTRU battery level is checked to determine if it is belowthe low level (step 552). If the battery level is above the low level,then rate reduction is performed (step 554) and the procedure terminates(step 549). If the battery level is below the low level, then ratereduction is not performed (step 556) and the procedure terminates (step549).

The WTRU battery measurement report can be a trigger of the user linkmaintenance procedure. If the RNC 104 receives a battery report message112 indicating a low battery level, the WTRU bit rate in the uplink isdecreased to reduce the battery consumption rate, which is especiallyuseful for long calls. The RNC 104 configures the WTRU 102 for a lowerbit rate (signal 142 in FIG. 1). In the downlink, the RNC 104 increasesthe bit rate transmitting to the WTRU 102, thus shortening the power-ontime of the WTRU 102. If the RNC 104 receives a battery report message112 indicating a battery level above the low level, and if the bit ratewas reduced before due to low battery, the link rate in uplink anddownlink will be restored to the previous rate before the last ratereduction.

In the downlink, if user link maintenance is triggered by anothermeasurement, for example, by code transmit power, the RNC 104 uses thebattery level of the WTRU 102 as an additional criterion for ratereduction. The criteria used depends on the design of the linkmaintenance control procedure 500, 520, 540. Different approaches inperforming link maintenance control may use different criteria. Forexample, the link maintenance control procedures described above useuplink WTRU transmit power and downlink code transmit power. If theWTRU's battery level is below the low threshold, decreasing the downlinkreceiving bit rate increases the time for the WTRU 102 to receive thesame amount of data, thus draining the WTRU 102 battery faster.Therefore, the link maintenance should not decrease the receiving bitrate for the WTRU 102.

In the uplink, if the user link maintenance is triggered by anothermeasurement, for example, by the WTRU transmit power, the RNC 104 usesthe battery level of the WTRU 102 as an additional criterion for raterecovery. If the WTRU's battery level is below the low threshold,increasing the uplink transmission bit rate drains the battery faster.Thus, the link maintenance should not increase the transmission bit ratefor the WTRU 102.

Handover

FIG. 6 shows a handover procedure 600 in accordance with the presentinvention. The RNC first receives a handover request (step 602) and thenchecks if there are additional handover requests waiting to be processed(step 604). If there are additional handover requests, the WTRU with thelowest battery level is selected (step 606). Next, the number of softhandover legs are determined, and the number is kept as low as possiblewhen operating in FDD (step 608). If, at step 604, there are noadditional requests, step 606 is skipped, and the procedure continueswith step 608. Lastly, the handover is performed (step 610) and theprocedure terminates (step 612).

A higher priority for handover is given to a WTRU 102 with a low batterylevel (signal 152 in FIG. 1). The battery level can be used to decidethe number of soft handover legs for FDD, where the lower the batterylevel, the fewer the number of handover legs that should be assigned. InFDD, the WTRU 102 can have simultaneous radio link connections (softhandover legs) in different cells. The more handover legs that areestablished, the faster the WTRU's battery will be consumed due to theextra processing needed for the extra handover legs.

Power Control

The BLER target is changed according to the WTRU battery level. At calladmission, the RNC RRM checks the service and determines the BLER targetbased upon the service type. The service type is the quality of serviceclass, for example, conversational, streaming, interactive/background,signaling AM/UM, or other service type. For each service type, there aretwo possible BLER targets for the RNC RRM when considering WTRU batterylevel.

The first possible BLER target is the “low quality BLER,” which is theminimum BLER acceptable by the network and can be used by the WTRU 102when its battery level is below the low threshold. The second possibleBLER target is the “high quality BLER,” which is better than the lowquality BLER and can be used by the WTRU 102 when its battery level isabove the medium threshold. A WTRU needs to transmit with higher powerin order to meet a high quality BLER target, so the battery needs tohave sufficient power to prevent a rapid depletion.

During a call, the power control is triggered based on the WTRU batterylevel (signal 162 in FIG. 1). An example of the numerical values both ofthe BLER target for several different service types is shown in Table 2.These values should be operations, administration, and maintenance(OA&M) configurable. The power control procedure can be triggered by thebattery level measurement report, as shown in steps 220 and 230 of FIG.2. TABLE 2 BLER target for different battery levels. Uplink BLERDownlink BLER Low High Low High Traffic Class Quality Quality QualityQuality Conversational 10⁻² 5 × 10⁻² 10⁻² 5 × 10⁻² Streaming 10⁻² 5 ×10⁻² 10⁻² 5 × 10⁻² Interactive/Background 10⁻³ 5 × 10⁻³ 10⁻³ 5 × 10⁻³Signaling AM/UM 10⁻³ 5 × 10⁻³ 10⁻³ 5 × 10⁻³

Application Configuration

For non-real time (NRT) calls, compression layers can be configured toprovide multiple levels of coding compression. Application configurationuses the battery level of the WTRU 102 as the only criterion todetermine the compression level. The lower the battery level, the higherthe level of compression that will be configured. At the applicationlevel, i.e., outside the UMTS terrestrial radio access network (UTRAN),the application can be optimized to provide different levels ofinformation. For example, in the case of a low battery level during Webbrowsing, the application can be configured to only allow the downloadof text and not pictures. The battery level measurement report cantrigger the application configuration procedure as described above inconnection with steps 224 and 234 of FIG. 2.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madewithout departing from the scope of the invention as describedhereinabove.

1. A method for congestion control in the uplink of a wirelesscommunication system having a wireless transmit/receive unit (WTRU) anda radio network controller (RNC), comprising the steps of: receiving aninterference report for each user; calculating the average noise risefor each user; and implementing congestion relieving measures based uponthe average noise rise and the WTRU battery level.
 2. The methodaccording to claim 1, wherein said implementing step includes the stepsof: comparing the average noise rise to a rate reduction threshold; andif the average noise rise is greater than the rate reduction threshold,then performing rate reduction for the user having the highestinterference level and terminating the method; if the average noise riseis less than the rate reduction threshold, then comparing the averagenoise rise to a rate recovery threshold; and if the average noise riseis less than the rate recovery threshold, then performing rate recoverybased upon the interference level and the WTRU battery level.
 3. Themethod according to claim 2, wherein said performing rate recovery stepincludes the steps of: ranking the users based on interference levelfrom lowest to highest into a candidate list; selecting the user withthe lowest interference level from the candidate list; checking theselected user's WTRU battery level; and if the battery level is belowthe low level, then performing rate recovery for the selected user andterminating the method; if the battery level is above the low level,then selecting the next user from the candidate list and repeating saidchecking step.
 4. A method for congestion control in the uplink of awireless communication system having a wireless transmit/receive unit(VVTRU) and a radio network controller (RNC), comprising the steps of:(a) receiving an interference report for each user; (b) calculating theaverage noise rise for each user; (c) comparing the average noise riseto a rate reduction threshold; (d) if the average noise rise is greaterthan the rate reduction threshold, then performing rate reduction forthe user having the highest interference level and terminating themethod; (e) if the average noise rise is less than the rate reductionthreshold, then (i) comparing the average noise rise to a rate recoverythreshold; and (ii) if the average noise rise is less than the raterecovery threshold, then (A) ranking the users based on interferencelevel from lowest to highest into a candidate list; (B) selecting theuser with the lowest interference level from the candidate list; (C)checking the selected user's WTRU battery level; and (D) if the batterylevel is below the low level, then performing rate recovery for theselected user and terminating the method; (E) if the battery level isabove the low level, then selecting the next user from the candidatelist and repeating step (e)(ii)(C).
 5. A method for congestion controlin the downlink of a wireless communication system having a wirelesstransmit/receive unit (WTRU) and a radio network controller (RNC),comprising the steps of: receiving a transmission power report for eachuser; calculating the transmission power for each user; implementingcongestion relieving measures based upon the average transmission powerand the WTRU battery level.
 6. The method according to claim 5, whereinsaid implementing step includes the steps of: comparing the averagetransmission power to a rate reduction threshold; if the averagetransmission power is greater than the rate reduction threshold, thencomparing the average transmission power to a rate recovery threshold;if the average transmission power is greater than the rate recoverythreshold, then performing rate recovery for the user with the lowesttransmission power and terminating the method; if the averagetransmission power is less then the rate reduction threshold, thenperforming rate reduction based upon the average transmission power andthe WTRU battery level.
 7. The method according to claim 6, wherein saidperforming rate reduction step includes the steps of: ranking the usersbased on transmission power from highest to lowest into a candidatelist; selecting the user with the highest transmission power from thecandidate list; checking the selected user's WTRU battery level; if thebattery level is below the low level, then performing rate reduction andterminating the method; if the battery level is above the low level,then selecting the next user from the candidate list and repeating saidchecking step.
 8. A method for congestion control in the downlink of awireless communication system having a wireless transmit/receive unit(WTRU) and a radio network controller (RNC), comprising the steps of:(a) receiving a transmission power report for each user; (b) calculatingthe transmission power for each user; (c) comparing the averagetransmission power to a rate reduction threshold; (d) if the averagetransmission power is greater than the rate reduction threshold, thencomparing the average transmission power to a rate recovery threshold;(i) if the average transmission power is greater than the rate recoverythreshold, then performing rate recovery for the user with the lowesttransmission power and terminating the method; (e) if the averagetransmission power is less than the rate reduction threshold, thenranking the users based on transmission power from highest to lowestinto a candidate list; (i) selecting the user with the highesttransmission power from the candidate list; (ii) checking the selecteduser's WTRU battery level; (iii) if the battery level is below the lowlevel, then performing rate reduction and terminating the method; (iv)if the battery level is above the low level, then selecting the nextuser from the candidate list and repeating step (e)(ii).